When it comes to textures, i allways found it practical to have a testing-texture just to see if my triangles are aligned correctly and to get a feeling about the translation from what i see in the world to the actual texture coordinates.
I did those grafics and perhaps someone will find them useful.
Maybe u want to add them to the default textures provided with jme?
This is a logical setup 256×256 pixel texture, every colorbar is exactly 16px; Its got 2 greys (0x00888888 and 0x00CCCCCC), all other colors are at their binary max (eg: yellow 0x00FFFF00), so it is easy to not only spot the coordinate down to a single pixel if you zoom close enough and remeber that the order is just black, rainbow, white but also to compare the resulting color with the input color. The borders have no rulers to not occlude tile seams.